Patent GB-921264-A (GB)
Title: Improvements in and relating to semiconductor devices
IPC: H01L21/00
Filed: 1960-05-02
Abstract: 921,264. Semi-conductor devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 2, 1960 [Aug. 5, 1959], No. 15286/60. Class 37. A semi-conductor device comprises a continuous PN junction of which part has an Esaki diode characteristic and another part a normal junction diode characteristic. The essential constructional features of an Esaki diode are that the valence band in the P-type region overlaps the conduction band in the N-type region, and that the distance between the regions is small enough to allow electrons to tunnel between the bands, e.g. 150  or less. In one example a transistor, Fig. 5, comprises degenerate P and N regions 15, 16, non-degenerate N and P regions 13, 12 and ohmic contacts 17, 18, 19. The emitter current-voltage characteristic 28a, 28b, between emitter contact 18 and base contact 17 is the sum of the characteristic 26a 26b, of an Esaki diode and that 27a, 27b, of a conventional diode, as shown in Figs. 6A and 6B. Fig. 6A represents the situation where the negative resistance of the Esaki diode is greater than the resistance of the conventional diode, and Fig. 6B where it is less. In the former case, for emitter currents less than I 1  changes in emitter current have no significant effect on the collector current which is primarily dependent on that part 27a of the emitter current flowing through the conventional diode part of the junction. For higher currents the transistor behaves in a conventional manner. Such a transistor may be used in an oscillator, as a switch, or as a level setter in which only input signals raising the emitter current above I 1  give an output signal. A diode as shown in Fig. 8 includes an ohmic contact to degenerate P+ zone 16 and an ohmic contact either to degenerate N+ zone 15 or to non-degenerate zone 13. This diode also has the characteristic of Fig. 6A or 6B and may be triggered between the stable parts of its characteristic by current or light. In a hook collector transistor, Fig. 16, the current multiplying junction has Esaki diode and conventional diode parts 59, 60. For low collector currents the bulk of the current flows in the Esaki diode portion which does not perform the multiplying function whereas at higher current values current is diverted to the multiplying conventional diode part of the junction. The transistor thus has low a for low emitter currents and high α for higher currents. The first step in making the device shown in Fig. 5 is to diffuse donor impurity into the surface of a non-degenerate P-type germanium body to produce a non-degenerate N-type region and an overlying degenerate N+ region. The resulting body is sliced and the N+ regions removed from one surface of each slice. Alternatively, a starting body consisting of non-degenerate P and N zones is used and tin-arsenic alloyed into the N-zone surface to produce a degenerate N+ surface zone 15 from which excess tin-arsenic is then removed. The latter method produces a sharper N+N junction. In either case a pellet or tin-gallium is next alloyed to the degenerate N+ surface zone by rapid heating and cooling to form a degenerate P+ region 16 extending through the surface zone into contact with the N-zone 13. Part of the N+ zone may subsequently be removed by etching to alter the area ratio of the Esaki and conventional parts of the junction to a suitable value. The Figs. 8 and 16 devices are made by modifications of this method. Specification 842,103 is referred to.